Vacuum control



June 18, 1963 w. c. MALLISON 25,395

PROCESS FOR BLENDING A HOT POLYESTER RESIN AND POLYMERIZABLE SOLVENTOriginal Filed July 1'7, 1959 7'0 V4CUl/M SYSTEM VACUUM CONTROL iINSTRUMEN VACUUM CONTZOL REFRIGERATED AFTEE CONDENSER OPT/0M4].

COOLANT INLET $04 VE'A/T VAPOR INITIAL sou 5m 1 04/1265 \msr J AIR BL 50VALVE curr//va KEITLE r/rrm W/TH COIL 02 JACKET HOT RES/N f/VLETP20655552? QES/N OUTLET INVENTOR. W/LL/AM CHAQLE'S MAM/501V ATTORNEYUnited States Patent Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprlnted in italics indicates the additions made by reissue.

This invention relates to a novel and expedient procedure for theblending of a hot polyester resin with a polymerizably reactive diluent.Still further, this invention relates to a technique for blending a hotpolyester resinous material with a normally-liquid polymerizablyreactive diluent.

One of the objects of the present invention is to blend a hot polyesterresinous material with a normally-liquid polymerizably reactive diluentin order to prepare such a resinous material for further processing. Afurther object of the present invention is to cut a hot polyester resincomposition with a normally-liquid polymerizably reactive diluent by atechnique which reduces processing time and results in a substantialeconomy in the procedure. These and other objects of the presentinvention will be discussed in greater detail hereinbelow.

The resinous materials used in the present invention are identified aspolyester resinous materials which result from the esterification of apolyhydric alcohol with an alpha, beta-ethylenically unsaturatedpolycarboxylic acid. All of these polyester resins are well known in theart but the processing of these resins by present and past procedureshave presented serious problems in handling the hot resin whichprocedures have added to the processing time and to the actual cost ofproduction. These polyester resins are generally identified as anunsaturated polyester resin inasmuch as said resin is prepared byreacting a polyhydric alcohol and preferably a dihydric alcohol with analpha, beta-ethylenically unsaturated polycarboxylic acid and preferablyan alpha, beta-ethylenically unsaturated dicarboxylic acid. Theunsaturated polyester resins used in the present invention are blendedwith a polymerizable monomer and upon proper catalysis are converted toa thermoset condition into such useful materials as laminates and thelike.

In the prior art, polyester resins are conventionally prepared byheat-reacting a polyhydric alcohol with an alpha, beta-ethylenicallyunsaturated polycarboxylic acid. In order to achieve substantiallycomplete esterification of the polycarboxylic acid with the polyhydricalcohol, heating is continued at elevated temperatures in the range ofabout 150 C. to about 250 C. until a relatively low acid number isachieved. There is no significant criticality in the acid numberalthough generally it is desired to continue the reaction until the acidnumber has dropped below 100 and preferably below about 40. It isfrequently conventional in certain instances to continue theesterification reaction until the acid number has dropped below 10. Toaccomplish this, it is generally desired to utilize the polyhydricalcohol in an amount calculated, on a stoichiometrical basis, to besufficient, and preferably in excess by to 30% of the amount required tocompletely esterify the polycarboxylic acid present. After theesterification has been completed to the selected acid number, the hotresinous material, having a temperature varying between about 150 C. and250 C., and more particularly as a rule between about 180 C. and 210 0.,requires cooling before it is cut with a polymerimbly reactive solvent.If the cutting operation is accomplished at elevated temperatureswithout the benefit of the process of the present invention, substantiallosses of the polymerizably reactive solvent will be experienced. On theother hand, the cooling operation consumes so much time that it adds tothe cost of production. The art then has been confronted with theproblem of blending the hot polyester resin with the reactive solventand has seemingly had to choose between losing some of the solvent as aresult of the volatilization or to undergo the costly procedure ofcooling the hot resin down to a temperature which would permit itsdilution with the solvent without suffering a loss due to saidvolatilization. A further complication enters the picture in cutting thehot resin with the solvent if no provision is made to cool the resinbefore cutting it with the polymerizably reactive solvent. Not only doesone run the risk of losing solvent through volatilization but one alsoruns the risk of experiencing premature polymerization of thepolymerizably reactive solvent. This latter effect is also undesirableand must be avoided. By the practice of the present invention, all ofthese shortcomings of the prior art are avoided. In the first place, thepolyester resin can be charged into the solvent immediately after it hasbeen completely esterified and without any significant cooling of theresin, without experiencing any loss due to volatilization, or any lossdue to premature polymerization of the reactive solvent. It can be seenfrom this that the technique of the present invention saves time andmaterials and produces a better product more quickly.

In the preparation of the polyester resins of the present invention, onemay utilize any of the polyhydric alcohols such as ethylene glycol,propylene glycol, diethylene glycol, dipropylene glycol, trimethyleneglycol, tetramethylene glycol, pinacol, arabitol, xylitol, adonitol,mannitol, glycerol, trirnethylol propane, trimethylol ethane, sorbitol,pentaerythritol, dipentaerythritol, or the alkane diols such asbutanediol-l,4, pentanediol-l,5, hexanediol-l,6, and the like. Thesepolyhydric alcohols may be used either singly or in combination with oneanother. It is generally preferred that the polyhydric alcohol used bepredominantly a dihydric alcohol although minor amounts up to about 10to 25% of higher hydric alcohols such as trihydric, tetrahydric,hexahydric alcohols may be used. In the unsaturated'polyester resins, itis generally desired that there be produced a linear polyester resinwith polymerizable sites available for cross-linking with thepolymerizably reactive monomer. For the purpose of making unsaturatedpolyester rcsins then, it can be seen that the diols, and moreparticularly the glycols, are preferred. When the blend of a dihydricalcohol with a polyhydric alcohol having more than two hydroxy groupsare utilized, the average functionality of the alcohols used should notbe significantly above about 2.25.

In the preparation of the polyester resins used in the process of thepresent invention, one may utilize such polycarboxylic acids as thosepolycarboxylic acids which are free of non-benzenoid unsaturationincluding phthalic acid, oxalic acid, malonic acid, succinic acid,glutaric acid, sebacic acid, adipic acid, pimelic acid, suberic acid,azelaic acid, tricarballylic acid, citric acid, tartaric acid, maleicacid, and the like. Obviously, these acids may be used either singly orin combination with one another and the anhydrides of said acids,whenever available, may be used either singly or in combination with oneanother or in combination with the acids. Among the alpha,beta-ethylenically unsaturated polycarboxylic acids which may be used inthe practice of the process of the present invention are maleic acid,fumaric acid, aconitic acid, itaconic acid, chloromaleic acid, and thelike. The anhydn'des of these acids may be used, whenever available.These acids and/or their anhydrides may be used either singly or incombination with one another. In the unsaturated polyester resins, it isdesirable to utilize the alpha, beta-ethylenically unsaturated acids inan amount approximating at least 20% by weight of the total weight ofthe polycarboxylic acids used and preferably in amounts varying betweenabout 25% and 65% by weight based on the total weight of polycarboxylicacid used, the balance being polycarboxylic acids free of non-benzenoidunsaturation.

When the polyester resin is cut with a polymerizably reactive solvent,said solvent is a normally-liquid monomeric material such as styrene,ring-substituted alkyl styrenes, such as ortho-methylstyrene,meta-methylstyrene, para-methylstyrene, ortho-ethylstyrene,parapropylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, or thering-substituted halo styrenes such as ortho-chlorostyrene,rnetabromostyrene, 2,4-dichlorostyrene, 3,4-dibromostyrene, and thelike. Additionally, one may make use of such normally-liquidpolymerizable monomers as diallyl phthalate, triallyl cyanurate,acrylonitrile, methacryonitrile, ethacrylonitrile, alpha-chloroacrylonitrile, and the like. If the polymerizable monomeric solvent hasa boiling point which exceeds about 250 C. which would be theapproximate maximum temperature of the hot polyester resin and if it isnot desired to utilize a mixture of polymerizable monomeric solventswherein one of the solvents has a boiling point below the temperature ofthe hot polyester resin, one can make use of a lower boiling inertorganic solvent in combination with the higher boiling polymerizablereactive monomeric solvent with equal efiiciency. For instance, if onewere to cut a hot polyester resin material with triallyl cyanuratehaving a boiling point above 250 C. at atmospheric pressure, one shouldutilize an inert solvent such as benzene having a boiling point of about80 C. in order that the heat of vaporization of the flashing benzenewould absorb the heat of the unsaturated polyester resin and in thatmanner permit the immediate dilution of the hot polyester resin withoutloss of monomeric solvent. In the event that an inert solvent isutilized in combination with the polymerizable monomer, whether lowboiling or high boiling, it will be desirable upon the completion of theaddition of the hot polyester resin to the cutting kettle to remove saidinert solvent. This can be accomplished very readily by flashing off theinert solvent and condensing the same but removing the condensed inertsolvent from the system instead of returning the same to the cuttingkettle.

The mode of addition of the hot polyester resin to the normally-liquidsolvent is not critical. The hot uncut resin may be introduced into thecutting kettle into which has been introduced a predetermined quantityof the solvent material. The amount of solvent material charged to thekettle prior to the introduction of the hot polyester resin is a matterof choice depending, for instance, on the desired formulation of theultimate resin material. For instance, one would predetermine the amountof polymerizably reactive monomeric solvent charged to the cuttingkettle based on the amount desired in the ultimate composition. Forthese polyester resin compositions in which the polyester containsresidues of alpha, beta-ethylenically unsaturated polycarboxylic acids,one may utilize between about parts by weight of the monomeric solventto about 90 parts of the unsaturated polyester resin up to about 60parts of the monomeric material to about 40 of the polymerizableunsaturated polyester resin. Preferably, one should use between about 25parts of the monomeric solvent to about 35 parts of the monomericsolvent with a corresponding 75 parts to about 66 parts of thepolymerizable unsaturated polyester resin.

The hot polyester resin immediately upon complete esterification will beconveyed directly to the cutting kettle. To avoid viscosity increasesdue to temperature drop, the hot polyester resin can be conveyed throughsteam jacketed pipes to the cutting kettle. It will be apparent that itis extremely desirable that the materials within the cutting kettle bekept under constant agitation during the cutting step in order toachieve uniform distribution of the resin in the solvent and in order tomaintain uniform heat distribution. To achieve this under optimumconditions, the hot uncut resin can be introduced into the cuttingkettle beneath the surface of the resident solvent and preferably at apoint substantially immediately below the agitator. This can beaccomplished by utilizing a steam jacketed pipe finger. Since thesolvent material is a polymerizably reactive monomeric solvent, it willbe desirable to incorporate therein a polymerization inhibitor, many ofwhich are known in the prior art. These polymerization inhibitors may beused in amounts varying from about 0.001% to about 3% by weight based onthe total weight of the polymerizable solvent. Illustrative of theconventional types of polymerization inhibitor which are used arehydroquinone, ortho-cresol, metacresol, para-cresol, 2,6-ditertiarybutyl-4-methyl phenol, orcinol, resorcinol, 2-chloro-5-hydroxy toluene,Z-amino- S-hydroxy toluene, and many others. The prior art asrepresented by the US. Patents 2,457,657, 2,480,928 and 2,632,751 isillustrative of further inhibitors which may be used in thepolymerizable solvent in the present invention. The cutting kettle isusually fitted with a coil or a jacket in order that the solvent can beheated to a temperature above room temperature such as at about 50 or 60C. in order that upon the addition of the hot polyester resincomposition that a too sudden cooling of the resin will be avoided.After the solvent has been charged to the cutting kettle in the requiredamount and heated to the selected temperature, a vacuum is applied tothe system and regulated at a value corresponding to the vapor pressureof the solvent at the desired cutting temperature. Allowance may be madefor the depression of the solvent vapor pressure as resin is added. Itis often advantageous to heat the solvent to its boiling point at thevacuum pressure. The hot resin may then be metered into the cuttingkettle at any selected rate but preferably at a rate which will notoverload the condenser superimposed above the cutting kettle which iscooled sufficiently to condense the solvent vapors and return thecondensed solvent to the cutting kettle. As the hot resin is introducedinto the solvent, evaporation of the solvent takes place, absorbing thesensible heat of the resin. Upon the volatilization of the solvent, thevacuum applied to the system permits the solvent vapors to pass into thecondenser where cooling converts the vaporous solvent back to the liquidform and upon being returned to the cutting kettle is available againfor cooling any additional resin to be added to the cutting kettle.

One of the preferred embodiments of the present invention which may bepracticed when the solvent contains a quantity of polymerizationinhibitor as is indicated hereinabove, one may provide an orifice orsimilar metering device for the purpose of feeding a measured quantityof air into the cutting kettle in order to supplement the inhibitingeifect of the polymerization inhibitor incorporated into thepolymerizable solvent. The amount of air that may be bled into thesystem during the cutting operation may be varied over a fairly widerange up to an approximate maximum of 400 cubic feet per minute for each3500 pounds of polymerizable monomer in the cutting kettle. Forfractional or multiple amounts of monomer present in the cutting kettle,the maximum amount of air bled into the system can be varied eitherupwardly or downwardly. There is no lower limit to the amount of airbled into the system inasmuch as one can operate the cutting techniquewithout bleeding any air into the system. Precaution should be taken toavoid bleeding so much air into the system so as to destroy or renderinefiectual the vacuum placed on the system. Preferably, one would bleedbetween 5 cubic feet and 20 cubic feet per minute into the system basedon 3500 pounds of polymerizable monomer in the kettle. For optimumresults, between about 8 cubic feet and 12 cubic feet per minute may bebled into the system per 3500 pounds of polymerizable monomer in thecutting kettle.

The temperature of the monomer in the cutting kettle can be varied overa fairly substantial range such as between room temperature, i.e., about25 C. and 100 C. and preferably between about 40 C. and 60 C. dependingupon the type of monomer utilized and the quantity utilized. The vacuumon the system will vary inversely with the temperature of the monomer inthe cutting kettle initially. For instance, at 25 C. the vacuum will beabout 1 mm. of pressure whereas at 100 C. the vacuum will be about 120mm. of pressure. At 40 C. the vacuum will be about mm. of pressure; at50 C. the vacuum will be about 20 mm. of pressure; at 60 C. the vacuumwill be about 30 mm. of pressure while at 70 C. the vacuum will be about45-50 mm. of pressure. The measurements of vacuum recited hereinaboveare given in absolute terms rather than in negative terms, i.e., avacuum of 60 mm. is 700 mm. below one standard atmosphere of pressure.The polymerization inhibitor incorporated into the reactive monomerserves its purpose as long as the monomer is in the liquid state.However, when the reactive monomer volatilizes, it leaves substantiallyall of the inhibitor incorporated into the liquid monomer remaining inthe liquid phase of the monomer. When the monomer is volatilized to thevapor state, it is desirable to bleed air into the vaporous monomer inorder to preclude the possibility of undesirable polymerization in thesystem, particularly in the condenser.

Reference is made to the accompanying drawing which is virtuallyself-explanatory. The cutting kettle is equipped with an agitator, asolvent charge inlet, an uncut resin inlet and a valve for removing thecut resin. The cutting kettle is additionally equipped with a coil orjacket. Optionally, the kettle is equipped with an orifice or a similarmetering device for feeding a measured quantity of air into the cuttingkettle, which air functions as a polymerization inhibitor for thevolatilized monomer, particularly in the condenser and in the conduitleading to the condenser. Superimposed above the kettle and connectedthereto by a two-way conduit is the condenser which is cooled bysuitable means such as water cooled coils and into which the volatilizedinhibited monomer is returned to the liquid state and passed back intothe cutting kettle. Above the condenser is the vacuum system completewith the conventional vacuum control valves and instruments. If desired,for a particular monomer, one could superimpose in the stream above thecondenser, a further condenser as indicated which would be refrigeratedwith a brine or the like in order to insure that there is no monomerloss.

In order that the present invention may be more completely understood,the following examples are set forth in which all parts are parts byweight. These examples are set forth primarily for the purpose ofillustration and any specific enumeration of detail contained thereinshould not be interpreted as a limitation on the case except as isindicated in the appended claims.

EXAMPLE 1 Into a suitable reaction vessel [equipped as] not shown in theaccompanying drawing, there is introduced 3 mols of phthalic anhydride,3 mols of furnaric acid and 6.6 mols of propylene glycol. With constantagitation, the charge is heated to about 210-220" C. and maintained atthat temperature until the esterification is substantially complete asindicated by an acid number of about 30-40. Just prior to the completionof the esterification reaction, there is introduced into a cuttingkettle 50 parts of monomeric styrene containing about 0.02% by weight ofditertiary butyl hydroquinone based on the weight of the styrene per 100parts of the unsaturated polyester resin being separately prepared. Thestyrene containing the inhibit-or is warmed to about 60 C.

whereupon with constant agitation there is introduced gradually over aperiod of time in a substantially constant stream parts of theunsaturated polyester resin thus prepared, and at a temperature of about210 C. A vacuum of 30 mm. of mercury was applied to the system justprior to the initiation of the introduction of the polyester resin intothe styrene. The hot polyester resin was introduced into the warmedstyrene monomer through a steam jacketed pipe finger directly under theagitator and below the surface of the styrene solvent in the cuttingkettle. As the hot polyester resin is being fed into the cutting kettle,there is bled into the system air in amounts approximating 8 cubic feetper minute per 3500 pounds of monomer in the cutting kettle. Themonomeric styrene becomes volatilized in part and passes through aconduit into the cooling condenser whereupon substantially all of thevaporized styrene is condensed and returned as liquid styrene to thecutting kettle. The time elapsed from the initiation of the introductionof the hot polyester resin into the styrene solvent is slightly over 1/2 hours whereas the average cutting time for a polyester resin of theexact same description and in the same quantity by conventionalprocedures is about 8 hours. Upon the completion of the addition of thehot polyester resin to the styrene solvent, the temperature of the blendhas reached about 60 C. and is then ready for further cooling andpackaging for sale.

I claim:

1. A process for blending a hot resin and a polymerizable solventcomprising introducing a hot polyester resin, at a temperature betweenabout 180 C. and 210 C. and prepared by reacting an aliphatic diol withan alpha, beta-ethylenically unsaturated dicarboxylic acid, into anormally-liquid polymerizable monomer containing a polymerizationinhibitor while maintaining the system under a vacuum evaporating themonomer to absorb the sensible heat from the hot resin and condensingthe gaseous monomer in a condenser and returning the liquid monomer thuscondensed to the blending vessel wherein said monomer in the mixingkettle initially has a temperature varying between about 25 C. and 100C. and the vacuum on said kettle during the polyester resin addition isvaried inversely with said monomer temperature between about 1 mm. andmms. [below atmospheric pressure] 2. A process for blending a hot resinand a polymerizable solvent comprising introducing a hot polyesterresin, at a temperature between about C. and 210 C. and prepared byreacting an aliphatic diol with an alpha, beta-ethylenica1ly unsaturateddicarboxylic acid, into a normally-liquid polymerizable styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, evaporating said styrene to absorb the sensible heat from thehot resin and condensing the gaseous styrene in a condenser andreturning said liquid styrene thus condensed to the blending vesselwherein said styrene in the mixing kettle initially has a temperaturevarying between about 25 C. and 100 C. and the vacuum on the kettleduring the polyester resin addition is varied inversely with saidstyrene temperature between aboult 1 mm. and 120 mms. [below atmosphericpressure.

3. A process for blending a hot resin and a polymerizable solventcomprising introducing a hot polyester resin, at a temperature betweenabout 180 C. and 210 C. and prepared by reacting an aliphatic diol withan alpha, betaethylenically unsaturated dicarboxylic acid, into styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, evaporating the styrene to absorb the sensible heat from thehot resin and condensing the gaseous styrene in a condenser andreturning the liquid styrene thus condensed to the blending vesselwherein said styrene in the mixing kettle initially has a temperaturevarying between about 25 C. and 100 C. and the vacuum on the kettleduring the polyester resin addition is varied inversely with saidstyrene temperature between about 1 mm. and 120 mms. [below atmosphericpressure] 4. A process for blending a hot resin and a polymerizablesolvent comprising introducing a hot polyester resin, at a temperaturebetween about 180 C. and 210 C. and prepared by reacting an aliphaticdiol with an alpha, beta-ethylenically unsaturated dicarboxylic acid,into a normally-liquid polymerizable monomer containing a polymerizationinhibitor while maintaining the system under a vacuum, while bleedingair into the blending vessel into the vaporous monomer so as to inhibitfurther the polymerization of the monomer, evaporating the monomer toabsorb the sensible heat from the hot resin and condensing the gaseousmonomer in a condenser and returning the liquid monomer thus condensedto the blending vessel wherein said monomer in the mixing kettleinitially has a temperature varying between about 25 C. and 100 C. andthe vacuum on said kettle during the polyester resin addition is variedinversely with said monomer temperature between about 1 mm. and 120 mms.[below atmospheric pressure] 5. A process for blending a hot resin end apolymerizable solvent comprising introducing a hot polyester resin, at atemperature between about 180 C. and 210 C. and prepared by reacting analiphatic diol with an alpha, beta-ethylenically unsaturateddicarboxylic acid, into a normally-liquid polymerizable styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, while bleeding air into the blending vessel into the vaporousstyrene so as to inhibit further the polymerization of said styrene,evaporating said styrene to absorb the sensible heat from the hot resinand condensing the gaseous styrene in a condenser and returning saidliquid styrene thus condensed to the blending vessel wherein saidstyrene in the mixing kettle initially has a temperature varying betweenabout 25 C. and 100 C. and the vacuum on the kettle during the polyesterresin addition is varied inversely with said styrene temperature betweenabout 1 mm. and 120 mms. [below atmospheric pressure] 6. A process forblending a hot resin and a polymerizable solvent comprising introducinga hot polyester resin, at a temperature between about 180 C. and 210 C.and prepared by reacting an aliphatic diol and with an alpha,beta-ethylenically unsaturated dicarboxylic acid, into styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, while bleeding air into the blending vessel into the vaporousstyrene so as to inhibit further the polymerization of the styrene,evaporating the styrene to absorb the sensible heat from the hot resinand condensing the gaseous styrene in a condenser and returning theliquid styrene thus condensed to the blending vessel wherein saidstyrene in the mixing kettle initially has a temperature varying betweenabout 25 C. and 100 C. and the vacuum on the kettle during the polyesterresin addition is varied inversely with said styrene temperature betweenabout 1 mm. and 120 mms. [below atmospheric pressure] 7. A process forblending a hot resin and a polymerizable solvent comprising introducinga hot polyester resin, at a temperature between about 150 C. and 250 C.and prepared by reacting an aliphatic diol with an alpha,betaethylenically unsaturated dicarboxylic acid, into a normally-liquidpolymerizable monomer containing a polymerization inhibitor whilemaintaining the system under a vacuum, evaporating the monomer to absorbthe sensible heat from the hot resin and condensing the gaseous monomerin a condenser and returning the liquid monomer thus condensed to theblending vessel wherein said monomer in the mixing kettle initially hasa temperature varying between about 25 C. and 100 C. and the vacuum onsaid kettle during the polyester resin addition is varied inversely withsaid monomer temperature between about 1 mm. and 120 mms. [belowatmospheric pressure] 8. A process for blending a hot resin and apolymerizable solvent comprising introducing a hot polyester resin, at atemperature between about 150 C. and 250 C. and prepared by reacting analiphatic diol with an alpha, beta-ethylenically unsaturateddicarboxylic acid, into a normally-liquid polymerizable styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, evaporating said styrene to absorb the sensible heat from thehot resin and condensing the gaseous styrene in a condenser andreturning said liquid styrene thus condensed to the blending vesselwherein said styrene in the mixing kettle initially has a temperaturevarying between about 25 C. and C. and the vacuum on the kettle duringthe polyester resin addition is varied inversely with said styrenetemperature between about 1 mm. and mm. [below atmospheric pressure] 9.A process for blending a hot resin and a polymerizable solventcomprising introducing a hot polyester resin, at a temperature betweenabout C. and 250 C. and prepared by reacting an aliphatic diol with analpha, beta-ethylenically unsaturated dicarboxylic acid, into styrenecontaining a polymerization inhibitor while maintaining the system undera vacuum, evaporating the styrene to absorb the sensible heat from thehot resin and condensing the gaseous styrene in a condenser andreturning the liquid styrene thus condensed to the blending vesselwherein said styrene in the mixing kettle initially has a temperaturevarying between about 25 C. and 100 C. and the vacuum on the kettleduring the polyester resin addition is varied inversely with saidstyrene temperature between about 1 mm. and 120 mms. [below atmosphericpressure] 10. A process for blending a hot resin and a polymerizablesolvent comprising introducing a hot polyester resin, at a temperaturebetween about 150 C. and 250 C. and prepared by reacting an aliphaticdiol with an alpha, beta-ethylenically unsaturated dicarboxylic acid,into a normally-liquid polymerizable monomer containing a polymerizationinhibitor while maintaining the system under a vacuum, while bleedingair into the blending vessel in the vaporous monomer above the liquidlevel in the vessel in order to inhibit further the polymerization ofthe monomer, evaporating the monomer to absorb the sensible heat fromthe hot resin and condensing the gaseous monomer in a condenser andreturning the liquid monomer thus condensed to the blending vesselwherein said monomer in the mixing kettle initially has a temperaturevarying between about 25 C. and 100 C. and the vacuum on said kettleduring the polyester resin addition is varied inversely with saidmonomer temperature between about 1 mm. and 120 mms. [below atmosphericpressure] 11. A process for blending a hot resin and a polymerizablesolvent comprising introducing a hot polyester resin, at a temperaturebetween about 150 C. and 250 C. and prepared by reacting an aliphaticdiol with an alpha, beta-ethylenically unsaturated dicarboxylic acid,into a normally-liquid polymerizable styrene containing a polymerizationinhibitor while maintaining the system under a vacuum, while bleedingair into the blending vessel into the vaporous monomeric material abovethe liquid level so as to inhibit further the polymerization of saidstyrene, evaporating said styrene to absorb the sensible heat from thehot resin and condensing the gaseous styrene in a condenser andreturning said liquid styrene thus condensed to the blending vesselwherein said styrene in the mixing kettle initially has a temperaturevarying between about 25 C. and 100 C. and the vacuum on the kettleduring the polyester resin addition is varied inversely with saidstyrene temperature between about 1 mm. and 120 mms. [below atmosphericpressure] 12. A process for blending a hot resin and a polymerizablesolvent comprising introducing a hot polyester resin at a temperaturebetween about 150 C. and 250 C. and prepared by reacting an aliphaticdiol with an alpha, beta-ethylenically unsaturated dicarboxylic acid,into styrene containing a polymerization inhibitor While maintaining thesystem under a vacuum. while bleeding air into the blending vessel intothe vaporous monomeric material above the liquid level so as to inhibitfurther the polymerization of said styrene, evaporating said styrene toabsorb the gaseous styrene in a condenser and returning said liquidstyrene thus condensed to the blending vessel wherein said styrene inthe mixing kettle initially has a temperature varying between about 25C. and 100 C. and the vacuum on the kettle during the polyester resinaddition is varied inversely with said styrene temperature between about1 mm. and 120 mms. [below atmospheric pressure] References Cited in thefile of this patent or the origmal patent UNITED STATES PATENTS GerhartJan. 3, 1950 Meeske et al. July 28, 1953 OTHER REFERENCES

